Preparation and properties of medium temperature membranes based on zirconium sulfophenylphosphate/sulfonated poly(phthalazinone ether sulfone ketone) for direct methanol fuel cells

Novel polymer composite membranes composed of sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) and inorgano-organic zirconium sulfophenyl phosphate (ZrSPP) were prepared by solution casting. Three ZrSPP concentrations were used: 10, 20 and 30 wt%. The degrees of sulfonation (DS) of SPPESK were 34.6% and 76%. The DS of ZrSPP was 95%. Membranes were characterized by infrared spectroscopy (IR), X-ray diffraction spectroscopy (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). IR results indicated intense hydrogen bonds formed between ZrSPP and SPPESK molecules. SEM micrographs showed that ZrSPP mixed well with SPPESK and formed dense structures. The proton conductivity of the 10 wt% SPPESK (DS 76%)/ZrSPP composite membrane reached 0.393 S/cm at 120 °C and that of the 30 wt% of SPPESK (DS 34.6%)/ZrSPP composite membrane reached 0.23 S/cm at 160 °C and 100% relative humidity (RH). Proton conductivities of the SPPESK/ZrSPP composite membranes were better than that of the Nafion®117 membrane in the temperature range of 80-160 °C. The methanol permeabilities of the SPPESK/ZrSPP composite membranes were in the range of 1.9 × 10−8 to 0.15 × 10−8 cm2/s, much lower than that of Nafion®117 (2.4 × 10−6 cm2/s). The composite membranes exhibited good thermal stabilities, proton conductivities, and good methanol resistance properties.